JP2015014081A - Caisson and construction method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a caisson capable of sufficiently resisting to floating-up of a caisson skeleton, only by constructing by pressing-in/sinking by a conventional method.SOLUTION: A blade port part 13 is provided on the lower end of the caisson skeleton 1 pressed/sunk in the ground, and a plurality of longitudinal rib-like fins 14 are arranged in a radial shape in a frame body 13a of the blade port part 13. An outer peripheral surface of the frame body 13a also becomes a skirt-like tapered surface. The lower end of the respective fins 14 is positioned under the lower end of the blade port part 13, and the respective fins 14 are formed in a cross-sectional wedge shape of becoming gradually smaller upward in its plate thickness. Thus, an opposed clearance Q formed of the mutual adjacent fins 14 is formed in a shape of becoming gradually smaller downward from above.

Description

  The present invention relates to an open caisson constructed by press-fitting / sinking in the ground and a construction method thereof, and more particularly to a caisson and a construction method thereof taking into account the rise of the caisson after construction / construction.

  For example, as a countermeasure against the lift of open caisson constructed with RC, PC well or steel segment, etc., the caisson chassis that was built up while assembling the steel segments, in addition to the caisson chassis itself that counteracts the lift. When it is assumed that its own weight is insufficient, as described in Patent Document 1, the anchor used at the time of press-fitting / sinking is effectively used to prevent the caisson housing from being lifted after construction. Things have been proposed.

JP-A-8-105054

  However, as represented by RC and PC well type caisson, when trying to counter the lift by the weight of the caisson body itself, the body volume increases with the outer diameter of the caisson body, resulting in an increase in the amount of excavated soil. This will increase the construction cost and make the construction period redundant.

  Moreover, in the technique described in Patent Document 1, after the caisson housing made of a steel segment is press-fitted / sunk, a bracket is attached to the ground portion of the caisson housing, and the bracket and the anchor steel used during press-fitting / sinking are used. It is necessary to connect the wire, which is not preferable because man-hours are inevitably increased.

  In addition, in many cases, the anchor used at the time of press-fitting / sinking needs to be removed permanently, and with the removal of the anchor, there is a possibility that the weight of the caisson housing cannot counter buoyancy. In that case, it is necessary to cast concrete having a required thickness on the inner peripheral side of the caisson casing made of steel segments, which is not preferable because it increases man-hours and makes the construction period redundant. In particular, in the case of the RC, PC well type caisson, when trying to secure the inner diameter dimension on the premise that concrete of the required thickness is placed on the inner peripheral side of the caisson housing made of steel segments as described above, Similarly, the volume of the caisson housing increases with the outer diameter of the caisson housing. As a result, the amount of excavated soil increases, leading to an increase in construction costs and redundancy of the construction period.

  The present invention has been made paying attention to such problems, and a caisson and a construction method thereof capable of sufficiently resisting the rise of the caisson housing simply by being constructed by press-fitting / sinking by a conventional method. It is to provide.

  The invention according to claim 1 is provided with a blade mouth portion at the lower end of the caisson housing press-fitted and set in the ground, and a plurality of protrusions are provided intermittently on the outer periphery of the blade mouth portion, The soil sandwiched between adjacent projections in the circumferential direction of the blade opening is constrained by applying a compressive force in the circumferential direction.

  More specifically, as described in claim 2, the upper dimension of the opposing gap formed by the adjacent protrusions in the circumferential direction of the blade edge part is set larger than the lower dimension. It is assumed that the soil sandwiched between the protrusions adjacent to each other in the circumferential direction of the blade edge portion is restrained by applying a compressive force in the circumferential direction.

  In this case, the caisson housing is assumed to be constructed of, for example, a segmented segment made of steel or concrete, in addition to RC and PC wells.

  Desirably, as described in claim 3, the facing gap formed by the adjacent protrusions is set to gradually decrease from the upper side to the lower side, and as described in claim 4. Suppose that the lower end of each above-mentioned projection part is located below the lower end of a blade mouth part.

  More preferably, as described in claim 5, in the plan view of the caisson housing, the cutting edge portion of the blade edge portion is arranged so that a line connecting the tips of adjacent protrusion portions does not contact the outer peripheral surface of the blade edge portion. Assume that the protruding amount of each protruding portion outward in the radial direction is set.

  Therefore, in at least the first aspect of the present invention, for example, the gap formed by the adjacent protrusions on the outer peripheral side of the blade edge portion is shaped so that the upper side is wider than the lower side. In this case, the earth and sand accommodated in the space between the protrusions is consolidated in the circumferential direction and downward while being given a compressive force in the circumferential direction of the blade portion 13 by a so-called “wedge effect”. In addition, the weight of the earth and sand above the installation position of each protrusion acts as an additional load on the earth and sand in the gap between the adjacent protrusions. Become.

  This is the earth and sand that is located between the line connecting the tips of the protrusions in the plan view of the caisson housing and the outer peripheral surface of the caisson housing, and corresponds to the total press-fitting / sinking amount of the caisson housing. Since the weight of the water reaches the caisson housing through the respective protrusions and blades, as a result, the weight of the earth and sand can be regarded as a part of the weight of the caisson housing.

  As a result, the apparent weight of the caisson housing is increased, and it is possible to prevent the caisson housing from being lifted after being press-fitted and set.

  According to the present invention, the soil sandwiched between the adjacent projecting portions in the circumferential direction of the blade edge portion is restrained by applying a compressive force in the circumferential direction, so that the projecting portions are moved upward. Sediment pressure acting on the caisson can be opposed to the buoyancy along with the weight of the caisson housing. As a result, the apparent weight of the caisson housing can be increased, so that the caisson housing can be prevented from being lifted after being pressed and set. become. And regardless of whether it is RC, PC well type caisson or split segment type caisson, the outer volume of the caisson body can be relatively reduced, resulting in less excavated soil volume, The construction cost can be reduced and the construction period can be shortened.

Explanatory drawing which shows the outline of an open caisson method. Cross-sectional explanatory drawing which shows 1st Embodiment of the caisson based on this invention. Plane explanatory drawing of FIG. The perspective view of the caisson shown in FIG. The principal part expansion explanatory drawing around the fin as a projection part shown in FIG. Functional explanatory drawing of adjacent fins as a projection part. Plane explanatory drawing which shows 2nd Embodiment of the caisson based on this invention. Plane explanatory drawing which shows 3rd Embodiment of the caisson based on this invention. Plane explanatory drawing of the caisson which concerns on a comparative example.

  FIGS. 1-6 shows the more concrete form for implementing the caisson based on this invention and its construction method, and especially FIG. 1 has shown the construction outline of the open caisson method using a PC well.

  In FIG. 1, 1 is a caisson housing in the middle of construction by press-fitting / sinking, 2 is a grip jack (press-fit jack) installed on the caisson housing 1 via a pressure girder 3, and 4 is a so-called heavy-weight clam shell 5 Each of the crawler cranes supported by suspension is shown.

  A ground anchor 6 is driven in advance around the caisson housing 1, and the ground anchor 6 is connected to the grip jack 2 via an anchor cable 7 and a rod 8. The caisson housing 1 is constructed by stacking circular concrete segments 1a (see FIG. 2) called PC wells, for example.

  When the grip jack 2 is extended as is well known, a pulling force is applied between the grip jack 2 and the ground anchor 6, and the reaction force is used as a press-fitting / sinking force to pressurize girders 3 and support girders 9. The caisson housing 1 is gradually press-fitted and laid down.

  By repeating such press-fitting / sinking and addition of the segment 1a to be the caisson housing 1, and excavation / soiling (so-called floor digging) of the inner bottom (bottom) in the caisson housing 1 by the clam shell 5, For example, as shown in FIG. 2, the caisson housing 1 is constructed to a predetermined depth. Here, when it is desired to recover the ground early, that is, to quickly recover the frictional force between the ground and the caisson housing 1, after the caisson housing 1 is press-fitted and set to a predetermined depth, It is desirable to inject and place contact grout in the gap. In FIG. 1, 10 is a hydraulic control device attached to the grip jack 2, and 11 is an attitude control device.

  FIG. 2 shows a caisson constructed by press-fitting and sinking the caisson housing 1 to a predetermined depth and then placing a bottom base concrete 12 on the inner bottom of the caisson housing 2. 3 is an enlarged plan view of FIG. 1, and FIG. 4 is a perspective view of the caisson of FIG.

  As shown in FIGS. 2 to 4, as is well known, a ring-shaped blade mouth portion 13 is attached to the lowermost portion (deepest portion) of the caisson housing 1 composed of a plurality of segments 1 a. It is made of concrete or steel. Then, a plurality of steel fins 14 are mounted on the outer periphery of the outermost annular frame 13a of the blade edge portion 13 as protrusions along the circumferential direction at an equal pitch or intermittently. is there. Each fin 14 has a sharp and plate-like shape with a sharpened lower end 14a, and is attached radially so as to be directed radially outward of the blade opening 13, and the lower end of each fin 14 has a blade opening. It is located further below the lower end of 13 itself.

  Regarding the frame body 13a of the blade edge portion 13, as shown in an enlarged view in FIG. 5, the outer peripheral cylindrical surface of the frame body 13a is formed into a skirt-shaped tapered surface having an angle θ so that the diameter gradually decreases upward. Is formed. Similarly, as shown in the expanded form in FIG. 6 with respect to each of the fins 14 described above, both the front and back surfaces, which are vertical wall surfaces of the fins 14, are inclined surfaces, and the plate thickness of the fins 14 is upward. It is formed as a wedge-shaped section that gradually decreases toward the end. Therefore, in the circumferential direction of the blade edge portion 13, the facing gap formed by the adjacent fins 14 has a shape that gradually decreases from the upper side to the lower side. That is, as shown in FIG. 5, in addition to the frame 13a being a tapered surface having an angle θ, as shown in FIG. 6, the upper end distance W2 and the lower end distance W1 between adjacent fins 14 are shown. As a relation, W1 <W2.

  Thus, in addition to the outer peripheral surface of the frame 13a being a tapered surface, each fin 14 is formed as a wedge-shaped section that gradually decreases in plate thickness upward, As shown in FIG. 6, the region (space) Q surrounded by the three of the frame body 13a and the two adjacent fins 14 attached to the frame body 13a gradually decreases or gradually decreases from the upper side to the lower side. It has a shape like this. As a result, the shape of the region (space) Q surrounded by the three of the frame body 13a and the two adjacent fins 14 attached to the frame body 13a has a substantially inverted truncated pyramid shape in three dimensions. Yes.

  Therefore, according to the caisson structure configured as described above, as shown in FIGS. 3, 4, and 6, the frame body 13 a and the two adjacent fins 14 attached to the frame body 13 a are provided on the outer periphery of the blade edge portion 13. The earth and sand possessed in the area (space) Q surrounded by the three of the above are the blades with the so-called “wedge effect” because the space Q itself has an inverted truncated pyramid shape as described above. While being compressed in the circumferential direction of the mouth portion 13 and being compressed in the circumferential direction and downward, it is constrained and held, and the earth and sand pressure (the weight of earth and sand) is that of the tapered surface that is the outer peripheral cylindrical surface of the frame 13a. In addition, it acts as a force for pushing down the blade opening 13 and thus the caisson housing 1 through the inclined surface of each fin 14. Further, the tip of each fin 14 is connected in the plan view of the caisson housing 1, as shown in FIG. The entire weight of the earth and sand having a width W3 formed by the outer periphery and the line M and the caisson housing 1 is applied as an overload of earth and sand held between adjacent fins 14.

  This means that the installation position of each fin 14 in the caisson housing 1 and the weight of all the earth and sand above it act as a force for pushing down the caisson housing 1 through the blade mouth part 13, in other words, the caisson housing. 1, the installation position of each fin 14 and the weight of all earth and sand above the fin 14 can be regarded as a part of the weight of the caisson housing 1. For this reason, the apparent weight of the caisson casing 1 is increased, and it is possible to prevent or suppress the caisson casing 1 from being lifted after being press-fitted and set.

  Here, as apparent from FIG. 6, for the purpose of the present invention, the protrusion is not necessarily limited to the plate-like fin 14 exemplified above. The point is that there are intermittently functioning as the projections similar to the fins 14 around the blade edge part 13, and when focusing on the opposing gap formed by these adjacent protruding parts, the opposing gap It is sufficient if the upper dimension is set to be larger than the lower dimension.

  FIGS. 7 and 8 show another embodiment of the caisson according to the present invention, and FIG. 9 shows a comparative example, both of which are the same enlarged plan views as FIG.

  As is clear from comparison with FIG. 3 which is the first embodiment, in FIG. 7, the number of fins 14 set on the outer periphery of the blade edge portion 13 is the same as that in FIG. The protrusion amount of the fin 14 to the radially outer side of the blade opening 13 is shorter than that in FIG. Further, in FIG. 8, the amount of protrusion of each fin 14 outwardly in the radial direction of the blade edge portion 13 is made the same as that in FIG. 3, and the number of fins 14 is reduced from that in FIG. .

  In addition to the structure of FIG. 3, in the structures of FIGS. 7 and 8, the line M connecting the tips of the adjacent fins 14 in plan view is set so as not to contact the outer peripheral surface of the caisson housing 1. As long as this condition is satisfied, the same effects as in FIG. 3 can be obtained in the case of FIGS.

  On the other hand, as shown in the comparative example of FIG. 9, the number of fins 14 set on the outer periphery of the blade edge portion 13 is smaller than that in FIG. If the protruding amount of the fins 14 is shorter than that in FIG. 3, the amount of earth and sand retained while being constrained by the facing gap Q between the adjacent fins 14 in FIG. 9 becomes extremely small, and the intended purpose cannot be achieved.

  Here, in the above-described embodiment, the caisson housing 1 constructed by assembling and stacking the circular concrete segments 1a called PC wells has been described as an example, but RC, PC well, steel or concrete made The present invention can be similarly applied to a caisson housing constructed using the divided segments.

DESCRIPTION OF SYMBOLS 1 ... Caisson housing | casing 1a ... Segment 13 ... Blade part 13a ... Frame 14 ... Fin (projection part)

In the invention according to claim 1, as a caisson structure , a blade mouth portion is provided at a lower end of a caisson housing press-fitted and set in the ground, and a plurality of protrusions are intermittently provided on the outer periphery of the blade mouth portion. The upper dimension of the opposing gap formed by the adjacent projecting parts in the circumferential direction of the blade edge part is set larger than the lower dimension .

Desirably, as described in claim 2, the facing gap formed by the adjacent protrusions is set to gradually decrease from the upper side to the lower side, and as described in claim 3. Suppose that the lower end of each above-mentioned projection part is located below the lower end of a blade mouth part.

More desirably, as described in claim 4, in the plan view of the caisson housing, the cutting edge portion of the blade edge portion is arranged such that a line connecting the tips of adjacent protrusion portions does not contact the outer peripheral surface of the blade edge portion. Assume that the protruding amount of each protruding portion outward in the radial direction is set.

According to the present invention, a plurality of protrusions are provided intermittently on the outer periphery of the blade edge at the lower end of the caisson housing, and the upper dimension of the opposing gap formed by adjacent protrusions in the circumferential direction of the blade edge Is set to be larger than the lower dimension, so that the soil sandwiched between adjacent protrusions in the circumferential direction of the blade edge portion is restrained by applying a compressive force in the circumferential direction. Therefore , the earth and sand pressure acting on these protrusions from above can face the buoyancy together with the weight of the caisson housing . As a result, it is possible to increase the apparent weight of the caisson housing, so that it is possible to prevent or suppress the caisson housing from being lifted after being press-fitted and set. And regardless of whether it is RC, PC well type caisson or split segment type caisson, the outer volume of the caisson body can be relatively reduced, resulting in less excavated soil volume, The construction cost can be reduced and the construction period can be shortened.

Claims (14)

There is a cutting edge at the lower end of the caisson housing that is press-fitted and submerged in the ground,
A plurality of protrusions are provided intermittently on the outer periphery of the blade portion,
A caisson that restrains soil sandwiched between adjacent projecting portions in the circumferential direction of the blade edge portion by applying a compressive force in the circumferential direction. The upper dimension of the opposed gap formed by the adjacent protrusions in the circumferential direction of the blade edge part is set larger than the lower dimension,
The soil sandwiched between projections adjacent in the circumferential direction of the blade edge portion is thereby restrained by applying a compressive force in the circumferential direction. caisson.   The caisson according to claim 2, wherein the facing gap formed by the adjacent protrusions is set to gradually decrease from the upper side to the lower side.   The caisson according to claim 3, wherein a lower end of each protrusion is positioned below a lower end of the blade opening.   In the plan view of the caisson housing, the projection amount of each projection to the radially outer side of the blade edge is set so that the line connecting the tips of adjacent projections does not contact the outer peripheral surface of the blade edge The caisson according to claim 4, wherein the caisson is provided. On the outer periphery of the blade edge portion, longitudinal rib-shaped fins are provided radially as protrusions,
4. The caisson according to claim 3, wherein each fin is formed as a wedge-shaped section whose thickness gradually decreases upward.   The caisson according to claim 6, wherein each fin is formed as a wedge-shaped cross section whose thickness is gradually reduced upward as both front and back surfaces are inclined surfaces.   The caisson according to claim 7, wherein the lower end of each fin is positioned below the lower end of the blade opening.   In the plan view of the caisson housing, the amount of projection of each fin outwardly in the radial direction of the blade edge portion is set so that the line connecting the tips of adjacent fins does not contact the outer peripheral surface of the blade edge portion. The caisson according to claim 8, wherein the caisson is.   The caisson according to any one of claims 1 to 9, wherein an outer peripheral surface of the blade opening portion is formed in a tapered shape so that the diameter gradually decreases upward.   The caisson according to any one of claims 1 to 10, wherein the caisson housing is formed by assembling divided segments. There is a cutting edge at the lower end of the caisson housing that is press-fitted and submerged in the ground,
A plurality of protrusions are provided intermittently on the outer periphery of the blade portion,
The upper dimension of the opposed gap formed by the adjacent protrusions in the circumferential direction of the blade edge part is set larger than the lower dimension,
A caisson construction method characterized in that the caisson housing is press-fitted and submerged in the ground with the blade edge part with the plurality of protrusions as the deepest part. There is a cutting edge at the lower end of the caisson housing that is press-fitted and submerged in the ground,
A plurality of vertical rib fins are provided radially on the outer periphery of the blade opening,
Each of the fins is formed as a wedge-shaped section whose thickness gradually decreases upward.
A caisson construction method characterized in that the caisson housing is press-fitted and submerged in the ground with the blade edge part with the plurality of fins attached as the deepest part.   14. The caisson construction method according to claim 12 or 13, wherein a grout is injected and placed in a space around the caisson housing after the press-fitting / sinking.

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